They are fantastic, and well worth the money.

One thing I've noticed with mine is that there is a significant delay in the speed with which they work. On a sunny morning th temperature has reached 25C before mine start to open. During the day they are fully open at anything above 22C, and in the evening, the temperature can be down at 10C before they are fully closed.

Worth keeping an eye on when you try to get the opimum temperature to set them at...